This invention relates to material handling apparatus of the kind wherein articles to be treated at a work station are conveyed in succession along a continuously movable, endless conveyor that extends to and beyond the work station. When an article requiring treatment in a work station is presented by the conveyor to a zone adjacent the work station, such article is stopped and transferred from the conveyor to the work station for treatment. Other articles on the conveyor then continue their movement past the occupied work station. When the treatment of the article is concluded, the treated article is returned to the conveyor. To ensure the provision of space on the conveyor to accommodate the treated article, those articles upstream from the transfer zone are stopped during return movement of the treated article to the conveyor. Thereafter, the stopped articles are released and they continue their movement along the conveyor.
The prior art contains many examples of mechanisms for transferring articles from a continuously movable, endless conveyor to a work station for treatment of the article, following which the treated article is returned to the conveyor. Typical of such prior art are U.S. Pat. Nos. 2,884,113; 3,088,197; 3,527,087; 3,631,967; and 3,648,819. These prior art mechanisms include means for stopping articles on the conveyor, but the stopping of an article is abrupt, rather than cushioned, thereby subjecting the stopping mechanism to possible damage and, in addition, subjecting workpieces supported by such articles to the possibility of being dislodged or shifted.
Another disadvantage of known prior art stopping mechanisms of the kind referred to is that the projection of a stop member into the path of an oncoming article on the conveyor sometimes effects engagement of the stop member with the lower surface of a conveyor-supported article. If such article is relatively light in weight, engagement between the article and the stop member may dislodge the article. If the article is relatively heavy, engagement of the article by the stop member may effect undue wear or damage to the stop member and its associated operating means.
The above mentioned objectionable characteristics of the known prior art stopping mechanisms have been overcome to a large extent by mechanisms of the kind disclosed in U.S. Pat. No. 4,144,960 and in co-pending application Ser. No. 224,255 a continuation of application Ser. No. 12,644, filed Feb. 16, 1979, both abandoned. Each of these mechanisms is constructed in such manner as to prevent dislodgment of an article from the conveyor or damage to the stop mechanism in the event the latter is projected toward the path of articles moving on the conveyor and engages an article other than the one to be stopped, and each of such mechanisms provides for the cushioned stopping of a selected article. In these mechanisms, however, the cushioning devices are independent of and in addition to the means by which the stop is projected and retracted, thereby necessitating the provision of multiple parts with the attendant expense in the manufacture, assembly, and maintenance thereof.